The University of California, San Diego Pediatric AIDS Clinical Trials Unit (UCSD PACTU) proposes to continue its participation in the Pediatric AIDS Clinical Trials Groups (PACTG) funded through the National Institute of Allergy and Infectious Diseases. The UCSD PACTU and its members have made important contributions to the development, implementation and dissemination of the PACTG research agenda and have hold leadership critical to the success of the Group. The accomplishments of our PACTU have been a result of the cooperative efforts of outstanding laboratory scientists and clinical investigators, dedicated research staff and a highly supportive community. The major contributions of our site to the PACTG include providing leadership at the national level and contributing expertise in anti-retroviral therapy, interruption of perinatal transmission, virology, immunology, pharmacology, opportunistic pathogens and adolescents, and the accrual of significant numbers of patients to clinical trials. UCSD investigators have led numerous protocols, served on a broad range of committees and contributed as members of many protocol teams. The UCSD PACTU has contributed to all of the major studies performed by the PACTG. It has taken part in intensive Phase I, I-II studies as well as large multi-center Phase III studies. It has established an outstanding program for the care, recruitment to clinical studies, and retention of HIV-pregnant women, children and adolescents. The UCSD PACTU has always been among the highest performing sites as assessed by patient accrual into clinical trials, quality of data and availability of specimens. Extension of the UCSD PACTU to include a subsite in Phoenix, Arizona has further expanded out Unit's ability to recruit pregnant women and children into clinical trials from the southwestern United States. We believe that the UCSD PACTU's record of past achievement and its plans for the future will assure that the Unit and its members will continue to make important contributions to all aspects of the PACTG scientific agenda.